In the late 1970s and early 1980s, American Telephone & Telegraph Company (AT&T) developed early species of common channel interoffice signaling (CCIS). CCIS is essentially a network architecture for a switched telephone network in which information about a telephone call is transmitted over high speed data links that are separate from the voice circuits that are used to transmit the signals of the call itself. Early in the development of common channel interoffice signaling, it was recognized that the interoffice data signaling links could be designed to provide high speed digital data that could first determine whether a call could be completed prior to assigning trunk capacity to set up the voice link. Thus, with common channel interoffice signaling the identity of the called number can be transmitted over the interoffice signaling data links from the originating central office to the terminating central office. The terminating central office is the central office that services the called number. If the called number is busy, data providing this information is transmitted back over the interoffice signaling link to the originating central office that locally provides an audible busy signal to the caller. Therefore, no long distance trunk capacity is occupied during this process, and the voice circuits remain free for other uses. If the called number is not busy, various devices in the network respond to the information about this call to assign interoffice trunks to set up a connection for the call. While the call is being set up the originating central office, based on a signal from the terminating central office, returns an audible ring back tone (RBT) to the caller. Once the called number is answered, an answer signal is passed from the terminating central office to the originating central office, the ring back tone is terminated, and the call is completed.
The public switched telephone network evolved in the 1980s to a complex and very versatile system, most of which supports and is controlled by a form of common channel interoffice signaling. The basics of this network were designed by AT&T. It is commonly referred to as the advanced intelligent network (AIN). Such an advanced intelligent network is shown in FIG. 1, and the advanced intelligent network forms the environment of the present invention.
In the modern intelligent public switched telephone network, the same signaling path described above that is used for basic call set up, take down and routing, is also used to provide enhanced custom calling features and to control the operation of billing equipment and maintain billing records. One enhanced calling feature that may be delivered by the advanced intelligent network is personal number service. Personal number service is described in detail in U.S. patent application Ser. No. 07/936,384, filed Aug. 26, 1992 and assigned to BellSouth Corporation, the assignee of the present invention.
Each subscriber to personal number service is assigned a personal number. In turn, call routing information in the form of a data base of one or more hierarchical lists of destinations based on the time of day and day of the week from each subscriber is input into the advanced intelligent network. The data base of call routing information may be maintained either at the service circuit node (SCN) of the advanced intelligent network or at the service control point (SCP) of the advanced intelligent network. For the purposes of the following discussion, the data base of call routing information will be considered to reside at the service control point. The hierarchy and composition of the destination lists may be changed by the subscriber, and the subscriber may enable an override or make a request to direct selected calls to a specific destination, as necessary.
Any call directed to a subscriber's personal number is identified as a personal number service call by a query sent to the service control point of the advanced intelligent network. Once the call is identified as a personal number service call, the source of the call is identified. The identification of the source of the call made in several ways. First, the calling line number of the call is identified and compared to entries in a data base containing correlated calling line number and identity information. Second, the subscriber may have provided the service control point with identity information corresponding to particular calling lines. For example, the subscriber may have designated persons using certain calling lines as priority callers. In addition, the caller may provide the service control point with identity information through the input of a particular code. The service control point recognizes the code as identifying a priority caller. If the service control point fails to find or the caller does not immediately provide such identity information, the caller is requested by a recording from the service control point to provide such information.
While the source of the call is being identified, the service control point selects a first destination from the hierarchical list of destinations. At the first destination, the service control point announces the identified source of the call and requests call disposition information as to the acceptance, formal rejection or passive rejection, such as a no answer, of the call. If accepted, the service control point in conjunction with the signal transfer point routes the call to the first destination in the ordinary fashion. If rejected, the service control point routes the call to the default destination selected by the subscriber. If there is no response frown the called party at the first destination, this lack of response is considered a passive rejection. The service control point then requests call disposition information from the next destination in the destination list according to the hierarchy selected by the subscriber. The service control point continues to request call disposition information from each sequential destination on the destination list until the call is accepted or until the last destination on the destination list is reached, at which point the call is routed to the last destination. Personal number service thus allows subscribers to use one personal number as a contact number for receipt of all communications including wireline, wireless, facsimile transmissions and pagers.
As noted above, personal number service can be used as a contact number for facsimile transmissions. Personal number service can thereby be used to route the facsimile transmission to a selected destination which has been selected by the subscriber and which has a receiving facsimile machine. Alternatively, the subscriber can designate that a facsimile transmission should be stored at the service circuit node for later retrieval. In order to store the facsimile transmission or to route a facsimile call to the designated facsimile destination properly, the advanced intelligent network must be able to recognize that the originating call is from a facsimile machine.
For an ordinary facsimile call that is not directed to a number designated for personal number service, the sending facsimile machine originates the call by first going off hook and then dialing the called party. Once the dialing operation has been completed, the sending facsimile machine begins generating a 1200 hz calling tone signal (CNG signal) indicating a non-aural transmission is contemplated. The CNG signal is periodic with a 0.5 second 1200 hz tone followed by 3.5 seconds of silence. Once the voice connection has been set up and the called party has answered, the CNG signal alerts the instrument at the called destination that it should respond to such a non-aural transmission. The CNG signal initiates the handshaking procedure which allows the two facsimile machines to communicate and send and receive the facsimile transmission.
In the circumstance of personal number service, the advance intelligent network should be able to recognize the existence of a facsimile transmission prior to making the selection of the call destination from the hierarchical list supplied by the subscriber or before storing the facsimile transmission for later retrieval. Conventionally, once the call is identified as a number designated for personal number service, the service switching point (SSP) central office switch of the calling party is connected by a line to the service circuit node of the advanced intelligent network. The service circuit node then sends an answer signal to the SSP central office switch over the same line. The SSP central office switch of the calling party opens a speech path over the line between the calling party and the service circuit node. The service circuit node sends the industry standard ring back tone (RBT) to the calling party from a tone generator located in the service circuit node. The RBT provides feedback to the calling party to assure the calling party that the advanced intelligent network is setting up the call. While the service circuit node is sending back the standard RBT to the calling party, the service circuit node also connects a facsimile port to the line in an effort to detect the CNG signal from the incoming call. If the service circuit node detects the CNG signal from the incoming call, it identifies the call as being a facsimile transmission. Depending on the subscriber's preference, the facsimile transmission is either stored at the service circuit node for later retrieval or the service circuit node instructs the SSP central office switch to transfer the call to the line designated by the subscriber for receipt of facsimile transmissions.
As is apparent from the foregoing description, the proper storage or routing of the facsimile transmission to the designated location of the subscriber's facsimile machine depends on the facsimile port in the service circuit node detecting the existence of the CNG signal from the incoming call. At present, studies have found that the success rate for detecting facsimile calls is only about 87% for such personal number service. Therefore, where personal number service is being used, a facsimile machine which initiates a call has a 13% chance of being connected in error to a voice call destination instead of being properly connected to the subscriber's designated facsimile destination or being properly connected to a facsimile port in the service circuit node for storage of the facsimile transmission for later retrieval.